text: Police verified that on the morning of May 13, the boys and girls of 3B class played and bit each other's hands?
classes:  No, two students had a conflict that led to biting each other on the morning of May 13.  Also, two students had a conflict that led to biting each other on the morning of May 13.  Yes, two students had a conflict that led to biting each other on the morning of May 13.